Conventional collision detecting sensors are disclosed in JP-A-2006-105973 (Reference 1) corresponding to EP 1795878A1 and in JP-A-2005-249680 (Reference 2) corresponding to US 2005/0193830 A1. The collision detecting sensor of Reference 1 includes an optical fiber and a corrugated plate, which are covered by a mold rubber. The collision detecting sensor of Reference 2 includes a concave holding member, a corrugated member arranged at the bottom of the holding member, an optical fiber arranged inside the concave holding member, and a counterpart member arranged so as to space from the holding member and the optical fiber at the initial state.
However, the sensor of Reference 1 needs to reshape the mold rubber by the press work after the mold rubber is extruded. If the mold rubber is pressed with the optical fiber is set in advance, the optical fiber may be broken. Therefore, for example, the mold rubber is pressed with a metal rod is set in advance, and after the metal rod is removed, the optical fiber needs to be inserted into a hole in which the metal rod was filled. Therefore, the manufacturing cost becomes high in the constitution that the optical fiber is covered by the mold rubber.
On the other hand, the sensor of Reference 2 can resolve the problem of the manufacturing cost since a mold rubber such as Reference 1 is not used. As described in Reference 2, the optical fiber is easily broken. According to Reference 2, when the excessive impact force is generated, since the impact is not transmitted to the optical fiber, the breakage of the optical fiber can be avoided. However, even though the impact force is small, when the optical fiber is pressed by the highly-rigid member directly, the optical fiber may be broken. To solve this problem, an outer surface of the optical fiber is covered by an elastic member such as a rubber. However, by the elastic force of the rubber which is attached to the outer surface of the optical fiber, the pressing force by the corrugated member is likely to be decreased and the sensitivity of the optical fiber is decreased.